The structure of chromatin will be examined at several levels: 1. Using reconstitution of core particles with DNA fragments of different sizes, we shall examine, by crosslinking of end-labeled short DNA fragments to histones, the location of histone-DNA binding sites. 2. Using radioactive-labeled protein crosslinkers, we shall map peptides crosslinked between histones. 3. "Hemisomes" will be prepared by reconstitution with 70 bp DNA, and their association-dissociation reactions, and histone homogeneity studied. 4. Reconstitution with longer DNA fragments will be used to assess cooperativity in core particle packing. 5. We will attempt to better delineate conditions under which core particle sliding can occur, and how H1 can be incorporated into reconstituted chromatin. 6. By modification of chromatin structure, we shall attempt to determine what factors are responsible for "phasing" of core particles. 7. Using yeast chromatin as a model, we shall attempt to examine the structure of an "active" chromatin at the nucleosome level.